The present invention relates generally to total knee arthroplasty (“TKA”). More specifically, this invention relates to an anterior stabilized posterior cruciate ligament (“PCL”) retaining total knee replacement prosthesis.
During articulation of a natural knee joint, flexion between the tibia and the femur takes place about a transverse axis while some relative rotation between the tibia and femur occurs about a longitudinal axis. Such flexion and rotation is necessary to carry out a normal gate cycle. Rotational stability of the natural knee is provided by the collateral and cruciate ligaments. Specifically, the anterior cruciate ligament (“ACL”) and PCL resist paradoxical movement in which the femur and tibia translate relative to each other in the posterior-anterior direction, while the collateral ligaments provide transverse stability of the knee joint. Further, all of these ligaments contribute to proprioception. When the natural knee joint is replaced by a total knee prosthesis, frequently either the ACL or both the ACL and PCL are removed.
A TKA that retains the PCL and removes the ACL, often called cruciate-retaining TKA, traditionally sacrifices the ACL such that the knee behaves as an ACL-deficient knee. This behavior may result in paradoxical movement during certain activities, such as physical activities utilizing a heel strike. Such paradoxical movement results in translation of the femur anteriorly with respect to the tibia until the collateral ligaments are tensioned to prevent further anterior motion.
A TKA that removes both the ACL and PCL and substitutes for the PCL is commonly known as posterior stabilized TKA. The most common form of PCL substitution is achieved by using a cam and post mechanism to substitute for PCL removal while, once again, characteristically sacrificing the ACL. Such devices primarily focus on the substitution of the PCL and consequently have characteristics of an ACL deficient knee such as anterior subluxation of the tibia in extension. Further, the removal of the PCL reduces proprioception, which may affect a patient's balance post-procedure.
Most recently, devices designated as “bicruciate substituting” have been designed, where both the ACL and PCL are removed and substituted. Certain of these devices utilize a post and cam mechanism to substitute for both the ACL and PCL. However, the removal and substitution of both cruciate ligaments reduces proprioception and natural knee function, particularly for the active individual. Further, the cam and post must remain engaged throughout flexion and extension, which may increase the likelihood of failure and wear.
Thus, currently available devices may sacrifice but not substitute for the ACL and may remove both cruciate ligaments limiting post-procedure proprioception. However, the ACL is an important ligamentous constraint for joint stability, and proprioception is important for balance particularly in more vigorous activities that require quicker response time. The result has been implants which generally function insufficiently for high levels of activity due to paradoxical movement and limited proprioception.
Therefore, there is a need for a total knee prosthesis that retains the PCL and provides the anterior stability necessary to support normal kinematics, improved proprioception, and that has reproducible and favorable long term results, particularly for the active patient.